Rotary or gerotor pumps have been used extensively in many different applications including automotive applications. Pumps such as those disclosed in Clark, U.S. Pat. No. 2,490,115, Obrist, U.S. Pat. No. 4,960,370, Brundage, U.S. Pat. No. 3,551,081 and Hill, U.S. Pat. No. 1,496,227 provide good pumping action powered by a central axis. Many of these pumps are specifically designed for automotive purposes.
A dual gerotor pump is a rotary pump which has two pumping chambers driven by the same shaft. These can be used in automotive applications with one pump pumping fluid to one vehicle system and a second pump pumping a second fluid to a second vehicle system.
In many applications the fluid pressure required is variable. An automatic transmission requires higher pressures under certain conditions such as during acceleration and lower pressures at other times. Driving at constant speed would require less. This is particularly true with continuous variable transmissions which utilize a belt and pulley system to vary the gear ratio. Such transmissions require a 60 to 800 psi difference.
The present invention is premised on the realization that a dual gerotor pump can be used to provide a wide range of fluid pressures for automatic transmissions and in particular constant variable transmissions. More particularly the present invention is premised on the realization that a dual gerotor pump having a primary pump constantly connected to the transmission and a secondary pump which can on demand be used to provide additional pressure to the transmission provides a superior range of pumping efficiencies for an automatic transmission of an automobile. By recirculating the fluid in the secondary pump when not needed, one can maintain optimum fluid pressure within the automatic transmission. Further, fluid pressure can be increased instantaneously when needed.
The objects and advantages of the present invention will be further appreciated in light of the following detailed descriptions and drawings in which: